Free-running oscillator



March 17, 1970 P. c. M LEOD, JR

FREE-RUNNING OSCILLATOR Filed May 10. 1967 FIG. I

FIG. 2

INVENTOR PAUL C. MCLEOD, JR.

ATTORNEYOQ,

United States Patent 3,500,849 FREE-RUNNING OSCILLATOR Paul C. McLeod, Jr., Little Rock, Ark., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York Filed May 10, 1967, Ser. No. 637,540 Int. Cl. F15c 1/08 US. Cl. 137--81.5 7 Claims ABSTRACT OF THE DISCLOSURE A free-running fluid oscillator including a single outlet port of approximately the same cross-sectional area, but axially offset slightly from an inlet nozzle located at opposite ends of a self-pressurized oscillator chamber.

BACKGROUND OF THE INVENTION Field of the invention The present invention has application to the field of gas chromatography wherein the frequency of a correctly designed fluid oscillator will change uniformly with a variation in the concentration of a heavier gas within a lighter gas stream. The invention has general application to fluidics where a simplified free-running oscillator is used to measure flow, pressure or temperature.

Description of the prior art Pure fluid devices have recently come into vogue and have a great application to sophisticated control systems and to computers generally, since the pure fluid devices are characterized by a total absence of moving parts. Free-running fluid oscillators have been devised which involve the alternate discharge of a power stream through adjacent outlet ports spaced downstream from the inlet nozzle. In these devices, the oscillation frequency is determined, in most part, by the configuration of the oscillator chamber. The known types of free-running fluid oscillator rely upon the wall attachment characteristic of the power stream discharging in jet form from the inlet nozzle into the oscillator chamber for effecting momentary discharge through one of the two chamber fluid outlets. To effect the switching, the known free-running fiuid oscillators are normally equipped with feedback passages which drain off a portion of the main power stream on the down stream side of the chamber and direct the same at right angles to the axis of the power stream as it enters the chamber through the inlet nozzle. Switching of the power stream from wall attachment on one side of the chamber to the opposite side causes discharge of the power stream alternately through the outlet ports.

The disadvantages of the conventional free-running fluid oscillator are readily apparent. With low flow rates, the velocity of the power stream jet is insuflicient to ensure stable oscillator operation; that is, the power stream jet may not only fail to lock onto one of the other cham her side walls, but if lock-on occurs, may not remain attached prior to switching as a result of normal feedback control. Further, in the conventional free-running fluid oscillator, the time required to initiate wall attachment of the jet may be detrimental to a desired. instantaneous operation, thus preventing conventional fluid oscillators from being used in particular applications.

SUMMARY OF THE INVENTION The present invention is directed to a simplified freerunning fluid oscillator including a closed fluid oscillator chamber, an inlet nozzle for directing a continuous power stream into one end of the chamber and a slngle chamber outlet port at the opposite end of the chamber.

3,500,849 Patented Mar. 17, 1970 ice The single fluid outlet port is offset axially and is of approximately the same cross-section as the power stream inlet nozzle. The configuration of the chamber and the axial oflset between the inlet nozzle and the single chamber outlet port creates a pressure differential across the power stream to effectively switch the power stream from one side of the chamber to the other side across the face of the single fluid outlet port.

In a preferred embodiment, the chamber end walls downstream of the power stream inlet and the corners of the chamber sections are curved to direct a portion of the power stream within the chamber sections initially rearwardly and then at right angles to the power stream near the inlet nozzle to alternately switch the power stream to the chamber sections in a conventional fluid oscillator fashion. If desired, each section of the oscillator chamber maybe vented to vary the frequency of the oscillator.

A BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a plan view, partially in section of a preferred embodiment of the free jet oscillator of the present invention.

FIGURE 2 is a plan view of a second embodiment of the present invention incorporating vents for each oscillator chamber section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The simplified free-running fluid oscillator of the present invention is shown in FIGURE 1. The construction of the fluid oscillator 10 is conventional. Fluidic devices in general consist of a laminar structure involving outer sheets or plates 12 and 14 acting to sandwich a configured intermediate sheet or plate 16. The laminae 12, 14 and 16 may be formed of metallic, plastic, glass, ceramics and glass ceramics or like material, with the outer sheets 12 and 14 being securely attached, in sealing relation, to the intermediate sheet 16 by suitable means, such as adhesive. The plates 12, 14 and 16 may be formed with suitable passages or apertures. If passages and internal apertures are formed in the outer plates 12 and 16, they must be formed to a depth less than plate thickness since these plates are also covers for the device. The plates 12, 14 and 16 are preferably bonded together by fusion. In the embodiment shown, the intermediate sheet 16 contains channels, passages, openings and the like. The re lieved or cut-out portion of the intermediate sheet may be achieved by stamping, etching or any other conventional process. In the structure shown, the intermediate sheet 16 has been cut away to form a fluid inlet line 18 terminating at inlet nozzle 20 at the upstream end of an oscillator chamber 22. An outlet port 24 is fluid coupled to the oscillation chamber 22 at the downstream end of the chamber and opens up into a tapered outlet channel 25. It is noted that axis 26 of the single outlet port 24 is offset slightly from axis 28 of the inlet nozzle 20, although the cross-sectional area of the inlet nozzle 20 at its entrance to chamber 22 is generally the same as the cross-sectional area of outlet port 24 at its connection point to the same chamber. While, in the plan view shown, the oscillation chamber 22 is generally rectangular in configuration, it is noted that for both chamber sections 30 and 32, the respective downstream walls 34 and 36 are curved, as well as the four corners 38, 40, 42 and 44 of the chamber. The chamber itself has an overall length from the upstream end to the dowstream end of approximately 15 to 20 times the width of the inlet nozzle 20 to provide the desired oscillator action.

It is obvious from this description that the free-running fluid oscillator of the present invention is considerably simplified when contrasted to prior fluid oscillators. It

has a single outlet port 24, no splitter and no walls for attachment or channels for feeback. The inlet nozzle and outlet port are axially offset by a distance indicated by arrow 46 on the order of one-half to one nozzle width. This allows the unit to begin pressure buildup in chamber section 30 at a low flow rate, allowing operation at jet velocities below that at which an unstable jet would cause it to begin. The oscillator in the form shown in FIGURE 1 operates on the basis of the pressure of circulating flow within the chamber sections, since there is no bleed and all of the fluid must exit through the single outport 24 is generally equal to or slightly larger than the power stream inlet nozzle 20. This maintains a high pressure in both chamber sections 30 and 32 at all times, while creating a pressure differential across the power stream 48 tending. to move through the chamber from inlet nozzle 20 to the offset outlet port 24. Assuming power stream 48 passes from a source (not shown) through inlet line 18 and inlet nozzle 20, initially, at least a portion of the power stream 48 impinges upon the downstream end 34 of chamber section 30, reversing its direction of flow as indicated by arrow 50. This creates a pressure differential across the power stream 4-8 discharging from inlet nozzle 20 to momentarily deflect the power stream across the face of outlet port 24 and into contact with the curved end wall 36 of the other chamber section 32. Immediately, the same type of operation occurs with respect to chamber section 32, causing a pressure differential tending to flip the power stream from chamber section 32 back to chamber section 30, again across the face of outlet port 24. The frequency of Oscillation between said chamber sections is determined by chamber configuration, flow velocity, and the characteristics of the fluid forming the power stream as well as other parameters. A generally high pressure is maintained in both chambers at all times due to the similarity in cross-sectional areas of inlet nozzle 20 and outlet port 24. If, however, the outlet port 24 is much larger in cross-section than the inlet nozzle 20, such that the chambers would not remain pressurized, acoustic reflections would undoubtedly control the switching from one chamber section to the other. The stream fluid 48 may be compressible, such as air, nitrogen, or other gases, or incompressible, such as water or other liquids. Both the compressible and incompressible fluids may contain solid material. This invention is not limited to any particular fluid. The present unit has been operated primarily on hydrogen and has been found to produce fluid pulses at a frequency from 50 to 120 kc. and at flow rates on the order of to 12 cubic centimeters per second. The actual switching frequency is one half of the measured frequency since the jet passes the outlet port 24 two times per cycle.

The free-running fluid oscillator of the present invention has definite application to the gas chromatography field. The frequency of a correctly designed fluid oscillator will change uniformly with a variation in the concentration of a heavier gas in a lighter gas stream, such as hydrogen. In the case of the present oscillator, the maximum sensitivity to a change in composition is on the order of 2400 cycles per second for instantaneous concentration of one percent methane in hydrogen. Other characteristics of a pressurized fluid readily affect the frequency of oscillation of the free-running oscillator. In addition to the use of the oscillator in gas chromatography, the oscillator may readily be used for the measurement of flow, pressure or temperature.

Turning to the embodiment of FIGURE 2, it is noted that the oscillator 10' is identical in all respects to the embodiment 10 of FIGURE 1, with the exception of the vent means for each chamber section. The oscillator 10 includes outer sheets 12 and 14' sandwiching intermediate sheet 16' which, in this case, has been etched to provide a central oscillator chamber 22 including chambe. i9 5 30' and 32'. Fluid inlet line 18 directs a pressurized fluid from a source (not shown) through inlet nozzle 20' at the upstream end of the chamber toward an axially offset outlet port 24' at the downstream end of the chamber. Port 52 connects with chamber section 30 for venting the same to the atmosphere. Circular port 54 performs a like function for chamber section 32. In this case, instead of subjecting the chamber sections to a continuous, rather high pressure and creating a slight pressure differential between chamber sections as a result of the presence or absence of main portion of the power stream within a particular chamber section, a somewhat greater pressure difference is created due to the presence of the vent ports.

The swirling action of the power stream within the opposite chamber creates a fluid force tending to shift the power stream itself from that chamber section into the opposing chamber section and past the face of the outlet port. In FIGURE 2, power stream 48' is, for instance, assume to have just switched such that the main portion of the stream 48' impinges upon curved end wall 36 of chamber section 32' causing it to change its direction and move towards the upstream end of the chamber where the curved wall 42' directs it generally at right angles against the power stream 48' as it enters the chamber from the inlet'nozzle 20' Instantaneously, due to the presence of vent port 52 in chamber section 30', there is a considerable pressure differential across the power stream between the chamber sections and the power stream will flip from chamber section 32 to chamber section 30 passing across the face of the outlet port 24'. Chamber section 32' is then vented to the atmosphere and the power stream impinging the curved downstream wall 34 of chamber section 30' reverses its direction to create a fluid pressure differential tending to flip the power stream back into chamber section 32'. The presence of the vent port 52 and 54 in the feedback chamber sections 30 and 32', respectively, has some effect on both the frequency and sensitivity of the oscillator of FIGURE 2 and possibly the acceptable flow rate range. By regulating the amount of fluid which is actually vented from the chamber, the oscillation frequency of the device may be readily changed.

While the present invention has been described in conjunction with a pressurized fluid in the form of a gas, water or other liquid may be readily substituted therefor.

What is claimed is:

1. A free-running fluid oscillator comprising: an oscillator chamber, a power stream inlet nozzle coupled to said chamber for directing a continuous power stream into said chamber, a single outlet port coupled to said chamber at the end opposite said inlet nozzle, said single outlet port being offset axially of said inlet nozzle, and feedback means formed by said chamber walls and comprising opposed chamber sections of appreciable volume on opposite sides of the power stream flow path for creating a pressure differential across the power stream to switch said power stream from one section of said chamber to the other, across the face of said outlet port.

2. The fluid oscillator as claimed in claim 1 wherein said outlet port is spaced downstream of said power stream inlet nozzle a distance on the order of 15 to 20 times the width of said chamber inlet nozzle.

3. The fluid oscillator as claimed in claim 1 wherein said outlet port is axially offset from said inlet nozzle a distance on the order of one-half to one times the width of said chamber inlet nozzle.

4. The fluid oscillator as claimed in claim 1 wherein the corners of said chamber are rounded to facilitate continuous oscillation of said power stream from one chamber section to the other across the face of said single outlet port.

5. The fluid oscillator as claimed in claim 1 wherein the cross-sectional area of said power stream inlet nozzle and said single outlet port is approximately the same.

6. The fluid oscillator as claimed in claim 1 further including vent means for said chamber.

7. The fluid oscillator as claimed in claim 1 further including means for venting each chamber section to the atmosphere.

References Cited UNITED STATES PATENTS 3,158,166 11/1964 Warren 13781.5 3,159,168 12/1964 Reader 13781.5

Fox et al 13781.5

Horton 13781.5 Warren et a1 13781.5 Unfried 137-815 Westerman 137-81.5 Boothe 13781.5

SAMUEL SCOTT, Primary Examiner 

